Overview
The K-Ride Alpine Ski Boot project, sponsored by Steven Sakofsky, focuses on improving upon the current design of alpine ski boots by increasing the allowed range of motion of the boot to allow lateral rotation and increasing forward rotation. In order to do this, the cuff portion of the boot was separated from the shoe, being rigidly attached to the leg. A gimbal design was incorporated to connect the cuff and the shoe. Sliders were added to accommodate for the difference in position of the pivot points on the gimbal versus the ankle of the wearer.
Major Components
Cuff
The cuff of the ski boot uses a rear entry system similar to that of snowboard boots. A slider rail is attached to the front of the cuff to allow the cuff to translate when the joint system bends. This is necessary due to the joint system's pivot differing in position from the pivot of the wearer's ankle.
Joint System
The joint system uses two off planar pivots that are perpendicular to each other, similar to a gimbal. The carriage to the slider on the cuff is attached to the back of the top joint in order to connect the cuff to the rest of the shoe.
Suspension
The suspension of the ski boot uses five compression springs. The springs compress when the wearer bends his/her leg and pushes the top joint down on the springs. This creates a restoring force on the user and gives the boot the desired stiffness for skiing. Additionally, bungee cords are attached between the top and bottom spring mounts between each spring to keep the springs in place as well as assist the springs in providing the sideways restoring force, since only half of the springs will be compressed when the wearer bends sideways.
Shoe
The shoe of the ski boot supports the bottom spring mount as well as the joint system. Although not shown in the CAD, a strap runs from the back of the shoe to strap the wearer's leg and ankle down onto the boot. Due to time and cost constraints, the shoe was the least developed of the main components. Many features would be quite similar to those of the current ski boot, therefore the project’s focus was on the joint and suspension system.
Conclusion
After testing the design, it was found that the gimbal and slider suspension system performed well for the forward flex, but needs improvement for the lateral flex. At small lateral angles, the boot performed as intended. However, at large lateral angles, the cuff would dig into the wearer’s leg, since the cuff would rotate at a different rate than the wearer’s leg due to the different pivot points of the wearer’s ankle versus the cuff. The system was analyzed statically and theoretical stiffnesses of the boot were found to be 0.7728 Nm/° (44.28 Nm/rad) for the forward flex and 0.3616 Nm/° (20.72 Nm/rad) for the lateral flex, which is less than half as stiff as the exoskeleton prototype.
For future designs, an extra slider can be added to the cuff of the boot to fix the difference in pivot points for the sideways pivot and the wearer’s ankle. For a stiffer suspension system, custom springs would need to be used since there are currently no purchasable springs that fit inside the spring mount and provide enough restoring force.